Determination of reactive hydrocarbons in air

ABSTRACT

REACTIVE HYDROCARBONS (RH) IN AUTOMOTIVE EXHAUST GASES ARE DETERMINED BY THE DIFFERENCES IN HEAT EFFECT OF COMBUSTION UPON THE GASES WITH AND WITHOUT THEIR CONTENT OF RH. PREFERABLY, THIS IS ACCOMPLISHED BY SUBJECTING A STREAM OF THE EXHAUST GASES TO COMBUSTION, THEN REMOVING THE RH FROM THE STREAM AND AGAIN SUBJECTING IT TO COMBUSTION, THE CONTENT OF REACTIVE HUDROCARBONS BEING DETERMINED AS A FUNCTION OF THE DIFFERENCE IN THE HEATS OF COMBUSTION BEFORE AND AFTER REMOVAL OF THE RH. THE RH REMOVAL IS EFFECTED BY PASSAGE OF THE GASES THROUGH A BODY OF ACID-RESISTANT GRANULAR MATERIAL IMPREGNATED WITH AN ANHYDROUS SOLUTION OF SULFURIC ACID AND AN ALKALI METAL DICHROMATE.

Jan. 26,1971 w. R. FREEMAN ETAI- 3,558,233

' DETERMINATION OF REACTIVE HYDROCARBONS IN AIR Filed June 9, 1967 SAMPLQ were:

, 7 a. mu 5M sue-r1014 J P-Y3 5 f NWER. PPLY EXHAUST GASES" Pows'tz SUPPLY FLAME IONIZATI ON EJ'E-CTQB STBIPPING COL UMN 1642 J 63%??? W12 1.10/9 2. P65501467.

United States Patent 3,558,283 DETERMINATION OF REACTIVE HYDROCARBONS IN AIR William R. Freeman, Pittsburgh, Pa., and Karl J. Bombaugh, Framingham, Mass., assignors t0 Mine Safety Appliances Company, Pittsburgh, Pa.

Filed June 9, 1967, Ser. No. 646,150 Int. Cl. G01n /22 US. Cl. 23-232 6 Claims ABSTRACT OF THE DISCLOSURE Reactive hydrocarbons (RH) in automotive exhaust gases are determined by the difference in heat effect of combustion upon the gases with and without their content of RH. Preferably, this is accomplished by subjecting a stream of the exhaust gases to combustion, then removing the RH from the stream and again subjecting it to combustion, the content of reactive hydrocarbons being determined as a function of the difference in the heats of combustion before and after removal of the RH. The RH removal is effected by passage of the gases through a body of acid-resistant granular material impregnated with an anhydrous solution of sulfuric acid and an alkali metal dichromate.

BACKGROUND OF THE INVENTION Air pollution workers believe that photochemical smogs are caused, at least in part, by photolytic ozonolysis of reactive hydrocarbons. They are therefore concerned with the removal of those hydrocarbons from automotive exhaust gases, at least to below an amount responsible for smog formation. Consequently, there are moves at both Federal and State levels not only seeking to limit the amount of RH emitted by automotive vehicles, but also to establish actual standards setting maximum permissible amounts. However, control of the allowable quantity of RH in exhaust gases is at present hampered by the lack of a simple method of measuring the amount of those hydrocarbons in the exhaust gases.

Various means and methods of minimizing air pollution and fog by automotive exhaust gases have been proposed and tried, but to date none has proved to be satisfactory for all conditions. Among the variety of proposals are those to pass the gases through oxidizing catalysts intended to convert the RH to innocuous compounds not productive of air pollution, to provide after-burners in the exhaust system, and various others.

It has been proposed also to substitute saturated compounds such as natural gas and liquefied petroleum gas (LPG) for the petroleum fuels now used because such saturated compounds are not productive of fog and smog.

A difliculty encountered with the use of catalytic systems, after-burners and related devices is that the content of RH in the exhaust varies with operating conditions such, for example, as whether the internal combustion engine is operating under normal or abnormal load, and differences in atmospheric conditions such as high and low humidity and variations in barometric pressure. The problem is complicated because the industry has lacked simple, reliable and relatively inexpensive means for monitoring the exhaust gases under all possible conditions. And although the substitution of natural gas or LPG would presumably solve the RH problem there would be encountered such factors as the necessity for storing enormous amounts of such gases under pressure which would involve cryogenic storage conditions and this involves great expense as well as the fire and explosion hazards attendant upon the storage and transmission of such gases.

Patented Jan. 26, 1971 It is among the objects of this invention to provide a method for the determination of reactive hydrocarbons (RH) in automotive exhaust gases which is rapid, simple, and operable by personnel not having technical training, is suited to field use as Well as at gasoline service stations, garages, inspection stations, and the like, and which make use of simple, relatively inexpensive, easily transportable apparatus consisting of standard equipment items and capable of visual, audible and recording response.

A further object is to provide a simple and inexpensive device for stripping RH from automotive exhaust gases.

THE DRAWINGS In the accompanying drawings FIG. 1 is a schematic representation illustrative of the preferred embodiment of the invention, and

FIG. 2 is a schematic representation of another embodiment.

DESCRIPTION OF THE INVENTION In accordance with the preferred embodiment of this invention a stream of automotive exhaust gases to be tested for its content of RH is introduced in a conduit 1, FIG. 1, Within which there are mounted electrically heated catalytic combustion filaments 2 and 3. The gases emerging from conduit 1 enter a conduit 4 and are passed through a column 5 capable of stripping the reactive hydrocarbons from the gas stream. The thus treated gases, now freed from RH, then pass through a conduit 6 to another conduit 7 containing electrically heated catalytic combustion filaments 8 and 9. Conduit 7 has an extension 7a from its outlet to a suction pump 10.

Electrical power is supplied to the apparatus by a supply 11, which may be one or more batteries in the case of portable equipment, from which conductors 12 and 13 establish a Wheatstone bridge-like circuit made up of the combustion filaments 2, 3, 8 and 9 and conductors 14, 15, 16 and 17. A sensitive meter 18 with conductors 19 and 20 completes the bridge circuit. Zero adjustment of the meter is accomplished in accordance with normal Wheatstone bridge practice by a rheostat 21 which serves to establish a null condition at the beginning of a test. Span adjustment to take care of different concentrations of RH is achieved through a rheostat 22. It should be pointed out that this embodiment is operative because only a small portion of the combustibles (RH) are consumed on the catalytic surfaces 2 and 3.

The stripping column of this invention consists of an elongated container, preferably of glass or other acidresistant transparent material, which contains a body of inert granular material impregnated with substantially anhydrous sulphuric acid (H having dissolved in it an alkali metal dichromate, preferably sodium dichromate (Na Cr O- Preferably also the acid used is preliminarily saturated with the dichromate, most suitably in initially dehydrated condition. Although it is preferred to use acidwashed diatomaceous earth as the carrier, a variety of other carrier materials are available such, for instance, as fire-brick, silica gel, alumina, and the like.

As as example of the preparation of a stripping col umn in accordance with the invention, sodium dichromate is dehydrated by heating at C. for four hours and it is then added to anhydrous sulphuric acid (reagent grade) in the proportion of 3 g. of the dehydrated dichromate to 40 cc. of the acid. The solution is allowed to stand until it assumes a dark red color, This aciddichromate solution is then thoroughly mixed with the inert carrier in the proportion of 24 g. of the acid solution to 60 g. of the inert carrier.

A stripping column adequate for use in a portable instrument in accordance with the invention may be prepared by filling a glass tube of 11 mm. diameter and six inches long with the impregnated carrier, and closing the ends of the tube with glass Wool plugs. An advantage of the device as thus described is that the appearance of a purple color in the column indicates the approach of exhaustion of the stripping material and thus shows the need for replacing the column with a fresh one.

In the use of the apparatus shown in FIG. 1 the exhaust gas to be tested is drawn by a pump into conduit 1 and passed over combustion filaments 2 and 3 after which it passes through the stripping column 5 and thence over the combustion filaments 8 and 9 followed by discharge to the atmosphere through conduit 7a. The circuit is such that the meter indicates the difference in heat of combustion of the gas stream before and after removal of the RH by the stripping column. Preliminary calibration using gases of known contents of reactive hydrocarbons will estabish a span setting so that the meter response will indicate the amount of reactive hydrocarbons in the gas being tested.

Although the invention has been described thus far with reference to passage of the exhaut gases through the system under reduced pressure, it will be clear to those familiar with the gas testing art that positive movement of exhaust gases through the system is equally applicable. Also, although the invention as thus described is based upon the use of the heats of combustion before and after removal of the reactive hydrocarbons, various other heat effects due to combustion may be used such, for example, as flame ionization in which the changes in ionization of a flame before and after removal of reactive hydrocarbons is applied to the same end.

Moreover, instead of subjecting a stream to combustion before and after removal of the RH, a stream of automotive exhaust gases may be split into equal portions one of which is subjected to combustion while the other is treated to remove the RH and then subjected to combustion using a similar system for obtaining the net effect of combustion of the two streams. FIG. 2 is illustrative of this embodiment. Here the stream of exhaust gases moves through a conduit 23 to a T having branches 24 and 25, one of which is provided with a regulating valve 26 for spitting the gas stream into two equal portions. From branch the gases pass to a flame ionization detector 27, a known type of device, where substantially all of the RH are consumed. The other branch stream passes first through a stripping column 28 of the type described above and thence to another flame ionization detector 29. After passage through detectors 27 and 29 the treated gases are exhausted.

Electric current is supplied to the detectors 27 and 29 from a source 30 from which leads 31 and 32 feed detectors 27 and 29 respectively. The outputs from these two detectors are passed to a summing amplifier 33, as shown. This is a standard piece of equipment. A suitable meter 34 associated with the amplifier shows the difference between the two input signals and hence is a measure of the RH content of the raw incoming exhaust gases.

There are, of course, other systems in which heat effects due to combustion may be applied for the same purpose, for instance, as determination of differences in thermal conductivity, various spectral determinations of the effect of heat upon streams with and without RH to determine the content of RH, and others. All such heat effects are within the purview of the invention. Also, instead of using a sensitive meter as a measuring instrument the output of the circuit may be used to actuate an audible or a visual signal, or both, when the content of reactive hydrocarbons reaches a predetermined value, or it may be applied to a recorder to provide a permanent record, all as will be understood by those concerned with such operations. Furthermore, combustion can be induced by means other than catalytic, e.g. by flame.

According to the provisions of the patent statutes, we have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to make it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. A method of determining the reactive hydrocarbon content of automotive exhaust gases comprising determining the heat effect of combustion upon a stream of the gases and also upon a stream from which the reactive hydrocarbons have been removed by passage through a body of acid-resistant granular material impregnated with a substantially anhydrous solution of sulfuric acid and an alkali metal dichromate, and applying the two heat effects to means responsive to the difference between them and thereby determining the reactive hydrocarbon content of the said gases.

2. A method according to claim 1, said dichromate being sodium dichromate.

3. A method according to claim 1, in which the acid is saturated with sodium dichromate dissolved therein.

4. A method of determining the reactive hydrocarbon content of automative exhaust gases comprising passing a stream of said gases into contact with electrically heated combustion filaments in opposed arms of a Wheatstone bridge, then removing the reactive hydrocarbons from the stream by passing said stream through a body of acidresistant granular material impregnated with a substantially anhydrous solution of sulfuric acid and and alkali metal dichromate and then passing ths stream over the opposed other arms of the same bridge and applying the output of the Wheatstone bridge to provide a measure of the amount of reactive hydrocarbons in the exhaust gases.

5. A method of determining the reactive hydrocarbon content of automotive exhaust gases comprising splitting a stream of said gases into two equal portions, subjecting one of said equal portions to combustion, removing the reactive hydrocarbons from the other of said equal portions by passing said other equal portion through a body UNITED STATES PATENTS 2,591,761 4/1952 Zaikowsky 73-27 2,633,737 4/1953 Richardson 73-27 3,026,713 3/1962 Block 73-27 3,237,181 2/1966 Palmer 73-27X 3,239,828 3/1966 Peterman 73-27X 3,224,838 12/1965 Evans 23-232 3,366,456 1/1968 Andreatch 23-230 OTHER REFERENCES A. Polgar, Organic Analysis, J. Mitchell, Jr. (ed), vol. III, 303, Interscience, New York, 1956.

W. B. Innes, Industrial Water and Wastes, 5 (6), 191 (1960).

JOSEPH SCOVRONEK, Primary Examiner S. MARANTZ, Assistant Examiner U.S. Cl. X.R. 

